The invention relates generally to fuel injected diesel engines and more particularly to direct injection type diesel engines having inverted fuel rocker mechanisms such as "V"-type engines suitable for use in locomotive, stationary and marine applications.
Improved engine efficiency has been a primary goal for diesel engine designers but has proved to be a difficult task particularly for older, larger and proven engine designs. With larger engines, a small fraction of a percentage increase in fuel efficiency can translate into a substantial cost savings over time. One such diesel engine is the ALCO Model 251 Series "V"-type diesel engine previously manufactured under license by Bombardier Inc. in Quebec, Canada and now manufactured by G.E. Canada in Quebec, Canada. Since purchases of large engines require a large capital investment, it is desirable that any change to facilitate engine efficiency improvement also minimize retrofit costs and preferably require little or no change to the engine block.
Known ALCO 251 diesel "V"-type diesel engines typically include a bank of combustion cylinders on a right side of the engine and a bank of combustion cylinders on the left side of the engine. Each cylinder typically has a corresponding piston and a plurality of cams. The cams typically include a fuel cam for moving a plunger inside a fuel pump to supply fuel to the cylinder, a corresponding air cam for moving air valves typically located in the cylinder head and a corresponding exhaust cam for moving exhaust valves also typically located in the cylinder head. The fuel cam contacts a roller of an inverted rocker arm to facilitate movement of the fuel pump plunger. The cams each have a cam profile and are rotatable about a cam shaft axis and are fixedly positioned with respect to each other to form a pre-determined cam orientation.
Such diesel engines have previously been designed with CQ type fuel pumps manufactured by Lucas Bryce, Gloucester, England, and small diameter multi-cylinder cam shafts which provided a fuel cam lift to fuel pump plunger lift ratio of less than 1:1. It was found that the reliability and efficiency of such engines was limited in part by the cam shaft configuration and the linkage from the cam shaft to the valves or fuel pump plunger.
Improved diesel engines have been designed to overcome some of these problems. These engines typically include unit cam sections that provide a 1:1 fuel cam lift to fuel pump plunger lift ratio to reduce loading on the cams and camshaft which increases reliability of the engine. The unit cam design also facilitates single cylinder cam replacement through an existing opening on the side of the engine instead of removing multiple cams for multiple cylinders longitudinally through the cam shaft bearing of the engine. Other improvements have also been made such as increasing the thickness of portions of the fuel pump support to further increase the rigidity of the cam to valve linkages and modifying the fuel cam profile to facilitate higher injection pressure. Another change included switching the fuel pump to a CV type fuel pump, also manufactured by Lucas Bryce, which was believed to have improved performance characteristics.
Although it has been found that fuel efficiency has been increased by nearly 1.5% after these improvements to the ALCO 251 diesel engine, further increases in fuel efficiency would be desirable to provide a low cost and easily installable alternative to purchasing and installing a new engine. Consequently there exists a need for improving diesel engine efficiency without requiring substantial changes to existing engine designs and which can be readily incorporated with existing engine blocks.